A074828 - OEIS

A074828

a(1) = 1; for n>1, a(n) = smallest composite multiple of n if n is a prime else the smallest prime divisor of n if n is composite.

1, 4, 6, 2, 10, 2, 14, 2, 3, 2, 22, 2, 26, 2, 3, 2, 34, 2, 38, 2, 3, 2, 46, 2, 5, 2, 3, 2, 58, 2, 62, 2, 3, 2, 5, 2, 74, 2, 3, 2, 82, 2, 86, 2, 3, 2, 94, 2, 7, 2, 3, 2, 106, 2, 5, 2, 3, 2, 118, 2, 122, 2, 3, 2, 5, 2, 134, 2, 3, 2, 142, 2, 146, 2, 3, 2, 7, 2, 158, 2, 3, 2, 166, 2, 5, 2, 3, 2, 178, 2

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OFFSET

1,2

COMMENTS

a(n) = 2n if n is a prime, a(2n+2) = 2.

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..20000

PROG

(PARI) A074828(n) = if(1==n, n, if(isprime(n), 2*n, factor(n)[1, 1])); \\ Antti Karttunen, Feb 06 2019

CROSSREFS

Cf. A020639.

Sequence in context: A021220 A195410 A095196 * A282028 A251561 A159193